Method for fabricating semiconductor device

Abstract

Disclosed is a method for fabricating a semiconductor device that improves a Self-Aligned Contact (SAC) margin by applying a wave-shaped buried gate. The method includes forming an isolation layer over a substrate and active regions defined by the isolation layer, forming a first hard mask pattern having a protrusion extending in a first direction over the substrate and overlapping with both ends of the active regions, forming a trench having a plurality of concave portions crossing the active regions and the isolation layer in the first direction and overlapping with the active regions by etching the substrate, and forming a buried gate structure to gap-fill the trench. The active regions are disposed in a first direction and a second direction orthogonal to the first direction and tilted in a third direction diagonal to the first and second directions.

What is claimed is: 
     
         1 . A method for fabricating a semiconductor device, the method comprising:
 forming an isolation layer over a substrate and a plurality of active regions defined by the isolation layer;   forming a first hard mask pattern having a protrusion extending in a first direction over the substrate and overlapping with both ends of the active regions;   forming a trench having a plurality of concave portions crossing the active regions and the isolation layer in the first direction and overlapping with the active regions by etching the substrate with the first hard mask pattern used as an etching barrier; and   forming a buried gate structure to gap-fill the trench,   wherein the active regions are disposed in a first direction and a second direction which is orthogonal to the first direction and tilted in a third direction which is diagonal to the first and second directions.   
     
     
         2 . The method of  claim 1 , wherein forming the first hard mask pattern includes:
 forming a first hard mask layer over the substrate;   forming a first mask pattern having a line shape extending in the third direction over the first hard mask layer;   forming a second mask pattern having a line shape extending in the second direction and spaced apart in the first direction over the first mask pattern;   forming an island-shape first mask pattern overlapping with both ends of the active regions that are adjacent to each other in the third direction by etching the line-shaped first mask pattern with the second mask pattern;   forming a third mask pattern having a line shape extending in the first direction and spaced apart in the second direction over the island-shape first mask pattern; and   forming a first hard mask pattern having a protrusion extending in the first direction and overlapping with both ends of the active region by etching the first hard mask layer with the third mask pattern and the island-shape first mask pattern.   
     
     
         3 . The method of  claim 1 , wherein forming the first hard mask pattern includes:
 forming a first mask pattern of a line shape extending in the third direction over the first hard mask layer;   forming a second mask pattern of a line shape extending in the first direction and spaced apart in the second direction over the first mask pattern;   forming an island-shape first mask pattern overlapping with both ends of the active regions that are adjacent to each other in the third direction by etching the line-shaped first mask pattern with the second mask pattern;   forming a third mask pattern of a line type extending in the first direction and spaced apart in the second direction over the island-shape first mask pattern; and   forming a first hard mask pattern having a protrusion extending in the first direction and overlapping with both ends of the active region by etching the first hard mask layer with the third mask pattern and the island-shape first mask pattern.   
     
     
         4 . The method of  claim 1 , wherein the protrusions are spaced apart from each other in the first direction along a first side and a second side of the first hard mask pattern. 
     
     
         5 . The method of  claim 4 , wherein the protrusion on the first side of the first hard mask pattern and the protrusion on the second side of the first hard mask pattern are not disposed on the same line extending in the second direction. 
     
     
         6 . The method of  claim 1 , wherein the concave portions are spaced apart from each other in the first direction along a first side and a second side of the trench. 
     
     
         7 . The method of  claim 6 , wherein the concave portions on the first and second sides of the trench are not disposed on the same line extending in the second direction. 
     
     
         8 . The method of  claim 6 , wherein the concave portions on first and second sides of the trench are disposed on the same line extending in the third direction that is non-orthogonal to the first and second directions. 
     
     
         9 . The method of  claim 2 , wherein the first to third mask patterns include a silicon material. 
     
     
         10 . The method of  claim 2 , wherein forming the first to third mask patterns includes using Double Spacer Patterning technology. 
     
     
         11 . The method of  claim 2 , wherein forming the first mask pattern includes a Positive Spacer Patterning technology that is performed twice. 
     
     
         12 . The method of  claim 2 , wherein forming the second and third mask patterns includes a Positive Spacer Patterning technology and a Negative Spacer Patterning technology. 
     
     
         13 . The method of  claim 1 , wherein a line width of the trench overlapping with the isolation layer is greater than a line width of the trench overlapping with the active region. 
     
     
         14 . The method of  claim 1 , wherein the trench is disposed one by one in each of the active regions. 
     
     
         15 . The method of  claim 1 , wherein
 after forming the buried gate structure,   the substrate is doped with an impurity to form a source region in the active region on a first side of the buried gate structure and to form a drain region in the active region on a second side of the buried gate structure.   
     
     
         16 . The method of  claim 1 , wherein the trench has a wavy line shape extending in the first direction. 
     
     
         17 . A method for fabricating a semiconductor device, the method comprising:
 forming a plurality of active regions over a substrate;   forming a first hard mask pattern having protrusions extending in a first direction over the substrate and overlapping with both ends of the active regions;   forming a trench having a plurality of concave portions overlapping with the active regions; and   forming a buried gate structure to gap-fill the trench,   wherein the active regions are disposed in first and second directions and are extending in a third direction which is non-orthogonal to the first and second directions.